Topical negative pressure (TNP) therapy has rapidly grown to be of excellent utility in the medical field, particularly in the treatment of wounds.
A number of the current negative pressure systems available involve the application of a porous, deformable wound filler to the wound. The basic principle of TNP therapy is to create a closed cavity over the wound itself by means of a thin, flexible sealing film adhered to the patient's sound skin surrounding the wound; admitting one end of an aspirant conduit into the closed cavity, the conduit being sealed to the flexible film, for example; and connecting a distal end of the aspirant conduit to a vacuum source such as an electrically driven vacuum pump, for example, to create a pressure lower than the surrounding ambient atmospheric pressure within the wound cavity. As is known to the skilled person the lower pressure creates many beneficial therapeutic effects on the wound including increased blood flow to the wound and faster granulation of tissue, for example. When the vacuum pump is switched on, the adjacent surfaces formed cavity expand into the wound filler, compressing it up to the point where it can mechanically resist further deformation. In this state, it is hypothesised that, in a wound cavity, both compressive and extensive forces are exerted on the micro scale at the tissue surface while extensive forces are exerted on the macro scale a short distance from the tissue-filler interface. The extent of these compressive and extensive forces is determined by the applied (negative) pressure, the mechanical properties of the surrounding tissue, filler and drape and the geometry of the wound.
One TNP system provide the user with sheets of foam of varying geometry that are routinely cut to shape at the site of application to conform to the surface of the wound or fill the wound cavity. In this regard, for some applications, including those targeted here, this technique is sub-optimal. The problem here is that even if we assume uniform foam, drape and tissue mechanics across the patient population, the wound geometry will vary significantly from patient to patient. FIG. 1 demonstrates the effect of applying standard pressure and mechanics (tissue, drape and foam) to varying geometries of application; the force vectors generated vary widely. For most applications, particularly to cavity wounds, the extent of this variation is not great and does not affect the efficacy of the treatment significantly: surrounding tissue is generally expanded in the desired direction, towards the centre line of the cavity volume (see FIG. 1). However, for shallow wounds or incisional wounds, the desired mechanical forces are not afforded by the current method; in general, a compressive force perpendicular to the tissue surface is generated with a minor force generated in the direction parallel to the wound surface. For shallow wounds and incision wounds, it is desirable to generate significant forces parallel to the wound surface in the direction of wound closure in the same way as it is desirable to generate this arrangement in wound cavities by the traditional method.
We are not aware of topical negative pressure devices capable of generating significant forces parallel to largely two-dimensional surfaces of attachment.